Line scanner that uses a color image sensor to improve dynamic range

ABSTRACT

A method for measuring 3D coordinates of points on a surface of an object by providing an articulated arm connected to a laser line probe. The laser line probe having a color camera sends color images to a processor, which determines 3D surface coordinates using triangulation. The processor weights each of the colors received from the pixels to enable dark and bright regions of the surface to be measured simultaneously.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims the benefit of U.S. Provisional PatentApplication No. 61/922,163, filed Dec. 31, 2013, the contents of whichare incorporated by reference herein.

FIELD OF THE INVENTION

The present disclosure relates to a laser line probe, and moreparticularly to a laser line probe having an improved high dynamic rangewith respect to its image capture capability.

BACKGROUND OF THE INVENTION

The three-dimensional (“3D”) physical characteristics of surfaces ofobjects may be measured using various non-contact techniques anddevices. Such measurements may be carried out for various reasons,including part inspection, rapid prototyping, comparison of the actualpart to a CAD model of the part, reverse engineering, 3D modeling, etc.Most often, these non-contact devices utilize triangulation-basedtechniques for processing the raw captured data representing the surfaceof an object into the resulting actual measurements of the objectsurface.

One type of triangulation-based, non-contact device is a laser lineprobe (“LLP”), which includes a projector and a camera. The projectorincludes a light source that emits a light, typically as a line. Thus,the LLP is also known as a line scanner. The projector also includes alens that projects the emitted light onto an object in a relativelyclear (unblurred) state. The emitted light may be laser light, partiallycoherent light, or incoherent light. The camera includes a camera-typeimaging device, such as a charge-coupled device (“CCD”) or CMOSphotosensitive array. The camera also includes a camera lens thatcaptures the pattern of light on the object surface and converts it intoa relatively clear (unblurred) state on the photosensitive array. Thecamera is typically positioned adjacent the laser light source withinthe LLP device. The projector has a virtual emission point from whichthe line or stripe of light appears to “fan out” in an angle in onedimension and in a flat sheet in the orthogonal dimension. The camerahas a camera perspective center through which rays of light from thepattern on the object appear to pass in traveling to the photosensitivearray. The line segment between the virtual emission point and thecamera perspective center is called the baseline, and the length of thebaseline is called the baseline length.

In some cases, the LLP is shaped as a hand-held device. In other cases,it may be attached to a motorized device or fixed in position on aproduction line. The fan of light that strikes the surface of the objectforms a relatively bright stripe of light on the object surface. Thecamera captures the 3D silhouette or profile of the laser stripeprojected onto the object. For the case of a hand-held LLP, to cover allor some portion of an object with the line of light, the LLP is moved bythe user such that the projected line stripe extends over all or atleast the desired portion of the object within the LLP's field of view.That way, by moving the LLP over the object, hundreds of cross sectionsof the object surface are captured as 3D point clouds of raw data. Somemodern LLPs can capture 60 frames, or stripes, of 3D data per second, orapproximately 45,000 points of data per second. Signal processingelectronics (e.g., a computer or a processor) are provided that runsoftware which processes the 3D raw point cloud data into the resulting3D image of the object that includes dimensional measurements asobtained by the LLP and its laser stripe and triangulation measurementprocess.

The image of the reflected line on the imaging device normally changesas the distance between the imaging device and the object surfacechanges. By knowing the baseline distance, the orientation of theprojector and camera with respect to baseline, and the coordinates onthe photosensitive array of the imaged pattern of light, knowntriangulation methods may be used to measure 3D coordinates of points onthe surface of the object. That is, as the LLP is moved, the imagingdevice sees each projected line stripe. Any deviations on thephotosensitive array from a straight line pattern may be translated intoheight variations on the object surface, thereby defining the objectsurface. In other words, the method described hereinabove digitizes theshape and position of the object within the field of view of the LLP. Inthis way the measured object may be checked against a CAD design modelof the same object to determine any discrepancies therebetween.

Portable articulated arm coordinate measuring machines (“AACMMs”) mayinclude a tactile probe configured to be brought into contact with anobject to determine 3D coordinates of the object surface. AACMMs havefound widespread use in the manufacturing or production of parts wherethere is a need to rapidly and accurately verify the dimensions of thepart during various stages of the manufacturing or production (e.g.,machining) of the part. Portable AACMMs represent a vast improvementover known stationary or fixed, cost-intensive and relatively difficultto use measurement installations, particularly in the amount of time ittakes to perform dimensional measurements of relatively complex parts.Typically, a user of a portable AACMM simply guides a “hard” contacttouch measurement probe (e.g., a ball) along the surface of the part orobject to be measured. The measurement data are then recorded andprovided to the user. In some cases, the data are provided to the userin visual form, for example, in 3D form on a computer screen. In othercases, the data are provided to the user in numeric form, for examplewhen measuring the diameter of a hole, the text “Diameter=1.0034” isdisplayed on a computer screen.

An example of a prior art portable AACMM is disclosed in commonlyassigned U.S. Pat. No. 5,402,582 (“the '582 patent”), which isincorporated herein by reference in its entirety. The '582 patentdiscloses a 3D measuring system comprised of a manually-operated AACMMhaving a support base on one end and a “hard” measurement probe at theother end. Commonly assigned U.S. Pat. No. 5,611,147 (“the '147patent”), which is incorporated herein by reference in its entirety,discloses a similar AACMM. In the '147 patent, the AACMM has a number offeatures including an additional rotational axis at the probe end,thereby providing for an arm with either a two-two-two or atwo-two-three axis configuration (the latter case being a seven axisarm).

It is generally known and accepted practice to attach a laser line probeto the probe end of an AACMM. The result is a fully integrated,portable, contact/non-contact measurement device. That is, the AACMMhaving an LLP attached thereto provides for both contact measurements ofan object through use of the “hard” probe of the AACMM and fornon-contact measurements of the object through use of the LLP's laserand imaging device. More specifically, the combination AACMM and LLPallows users to quickly inspect or reverse engineer complex and organicshapes via laser scanning, as well as to capture prismatic elements withthe relatively high accuracy that contact metrology provides.

When combined as such, the AACMM and LLP may have the LLP carry out someor all of the processing of the 3D captured point cloud data using thesignal processing electronics (e.g., computer or processor) within orassociated with (e.g., located apart from) the AACMM. However, the LLPmay have its own signal processing electronics located within the LLP orassociated with the LLP (e.g., a stand-alone computer) to perform thenecessary signal processing. In this case, the LLP may need to connectwith a display device to view the captured data representing the object.Also, in this case the LLP may operate as a stand-alone device withoutthe need to connect with an AACMM or similar device.

One important characteristic of any laser line probe is the dynamicrange of the imaging device within the LLP. Simply put, the dynamicrange of the imaging device is the range bounded on one end by theamount of relatively bright object surface portions that the imagingdevice is capable of accurately capturing and bounded on the other endby the amount of relatively dark object surface portions that theimaging device is capable of accurately capturing. Stated another way,the dynamic range of an imaging device is the ratio of the largestnon-saturating input signal to the smallest detectable input signal.Dynamic range essentially quantifies the ability of an imaging sensor toadequately image both the highlights and the dark shadows of an objector of a larger scene. A typical real-world object or scene desired to beimaged may have a wide range of brightness values (or contrastvariations) across the object surface or surfaces depending, in part, onthe ambient light illuminating the object at any one point in time. Forexample, it is not uncommon for an object or scene to vary in brightnessby 100 decibels or more.

The dynamic range required of an LLP for optimal determination of 3Dcoordinates of a surface is equal to the ratio of reflected opticalpower from the most reflective to the least reflective portions of anobject surface. Dynamic range may be described as a linear ratio or,more commonly, as a logarithmic ratio in units of decibels (“dB”). Therequired dynamic range for a particular measurement depends partly onthe material, color, and surface finish of the object surface, partly onthe distances from a surface point to the projector and camera, andpartly on the angles of incidence and reflectance of the projected andreflected light, respectively.

The dynamic range of an image sensor is the ratio of the largest opticalenergy to the smallest optical energy received by a sensing elementwithin the image sensor. To provide a valid reading, the dynamic rangereceived by a sensing element should be within the linear range of thesensing element, which is to say that the energy cannot be as large asto saturate or so small as to be noise limited. To perform at an optimallevel, the dynamic range of the imaging device should be equal to orgreater than the dynamic range required of a particular measurement.Most commercially available imaging devices, e.g., CCD's or CMOSimagers, have a dynamic range less than 100 decibels.

An LLP with a relatively low dynamic range imaging device (e.g., a CCDcamera or CMOS photosensitive array) results in a reproduced image thatmay be too dark is some areas and/or too light (i.e., saturated) inother areas. Thus, it may be difficult, if not impossible, to accuratelydetermine 3D coordinates with such an LLP.

As a result, many devices and techniques exist in the prior art forextending or increasing the dynamic range of imaging devices. However,these techniques and devices tend to be lacking somewhat in the amountof increase in the dynamic range of the imaging device.

While existing laser line probes are suitable for their intendedpurposes, what is needed is a laser line probe having an imaging devicewith improved (i.e., increased) high dynamic range.

SUMMARY OF THE INVENTION

According to one aspect of the invention, a method is provided formeasuring three-dimensional (3D) coordinates of points on a surface ofan object by providing a 3D coordinate measurement device, the deviceincluding a manually positionable articulated arm portion having opposedfirst and second ends, the second end coupled to a base, the arm portionincluding a plurality of connected arm segments, a laser line probe, andan electrical circuit, each of the arm segments including at least oneposition transducer configured to produce a position signal, the laserline probe coupled to the first end, the laser line probe including aprojector and a camera, the projector separated from the camera by abaseline, the baseline being a line segment, the projector configured toproject a line of light onto the surface, the camera including a lensand photosensitive array, the camera configured to form an image on thephotosensitive array of the line of light projected onto the object, thephotosensitive array having a plurality of pixels, each pixel configuredto provide electrical signal levels for a plurality of colors, thecamera configured to send the electrical signal levels from the pixelsto the electrical circuit, the electrical circuit including a processor;projecting the line of light onto the surface; forming a color image ofthe line of light on the photosensitive array; sending to the electricalcircuit an electrical signal in response to the color image, theelectrical signal containing a signal level for each of the plurality ofcolors for each of the plurality of pixels; determining with theprocessor an effective illumination level for each pixel, the effectiveillumination level for each pixel based at least in part on the signallevel for that pixel for each of the plurality of colors; anddetermining with the processor the 3D coordinates of points on thesurface, the 3D coordinates based at least in part on a length of thebaseline, an orientation of the projector to the baseline, anorientation of the camera to the baseline, the effective illuminationlevel for each pixel, and the position signals.

BRIEF DESCRIPTION OF THE DRAWINGS

Referring now to the drawings, exemplary embodiments are shown whichshould not be construed to be limiting regarding the entire scope of thedisclosure, and wherein the elements are numbered alike in severalFIGURES:

FIGS. 1A and 1B are perspective views of a portable articulated armcoordinate measuring machine (“AACMM”) having embodiments of variousaspects of the present invention therewithin;

FIG. 2, including FIGS. 2A-2D taken together, is a block diagram ofelectronics utilized as part of the AACMM of FIGS. 1A and 1B inaccordance with an embodiment;

FIG. 3, including FIGS. 3A and 3B taken together, is a block diagramdescribing detailed features of the electronic data processing system ofFIG. 2 in accordance with an embodiment;

FIG. 4 is an isometric view of the probe end of the AACMM of FIGS. 1Aand 1B;

FIG. 5 is a side view of the probe end of FIG. 4 with the handle beingcoupled thereto;

FIG. 6 is a side view of the probe end of FIG. 4 with the handleattached;

FIG. 7 is an enlarged partial side view of the interface portion of theprobe end of FIG. 6;

FIG. 8 is another enlarged partial side view of the interface portion ofthe probe end of FIG. 5;

FIG. 9 is an isometric view partially in section of the handle of FIG.4;

FIG. 10 is an isometric view of the probe end of the AACMM of FIGS. 1Aand 1B with a laser line probe having a single camera attached;

FIG. 11 is an isometric view partially in section of the laser lineprobe of FIG. 10;

FIG. 12 is a partial perspective view and partial schematic view of anembodiment of the present invention having an array of photodetectorswith integrated color filters and a color filter located on top of thearray;

FIG. 13 is a block diagram showing a portion of an embodiment in whichthe red, green and blue images of an object from a color camera areprocessed to provide an overall image of the object with increased highdynamic range;

FIG. 14 is a block diagram showing that the processing in FIG. 13 isperformed using an artificial neural network; and

FIG. 15 is a plot of the quantum efficiency of three color filterregions of a photosensitive array.

DETAILED DESCRIPTION

FIGS. 1A and 1B illustrate, in perspective, an articulated armcoordinate measuring machine (“AACMM”) 100 according to variousembodiments of the present invention, an articulated arm being one typeof coordinate measuring machine. As shown in FIGS. 1A and 1B, theexemplary AACMM 100 may comprise a six or seven axis articulatedmeasurement device having a probe end 401 that includes a measurementprobe housing 102 coupled to an arm portion 104 of the AACMM 100 at oneend. The arm portion 104 comprises a first arm segment 106 coupled to asecond arm segment 108 by a first grouping of bearing cartridges 110(e.g., two bearing cartridges). A second grouping of bearing cartridges112 (e.g., two bearing cartridges) couples the second arm segment 108 tothe measurement probe housing 102. A third grouping of bearingcartridges 114 (e.g., three bearing cartridges) couples the first armsegment 106 to a base 116 located at the other end of the arm portion104 of the AACMM 100. Each grouping of bearing cartridges 110, 112, 114provides for multiple axes of articulated movement. Also, the probe end401 may include a measurement probe housing 102 that comprises the shaftof the seventh axis portion of the AACMM 100 (e.g., a cartridgecontaining an encoder system that determines movement of the measurementdevice, for example a probe 118, in the seventh axis of the AACMM 100).In this embodiment, the probe end 401 may rotate about an axis extendingthrough the center of measurement probe housing 102. In use of the AACMM100, the base 116 is typically affixed to a work surface.

Each bearing cartridge within each bearing cartridge grouping 110, 112,114 typically contains an encoder system (e.g., an optical angularencoder system). The encoder system (i.e., transducer) provides anindication of the position of the respective arm segments 106, 108 andcorresponding bearing cartridge groupings 110, 112, 114 that alltogether provide an indication of the position of the probe 118 withrespect to the base 116 (and, thus, the position of the object beingmeasured by the AACMM 100 in a certain frame of reference—for example alocal or global frame of reference). The arm segments 106, 108 may bemade from a suitably rigid material such as but not limited to a carboncomposite material for example. A portable AACMM 100 with six or sevenaxes of articulated movement (i.e., degrees of freedom) providesadvantages in allowing the operator to position the probe 118 in adesired location within a 360° area about the base 116 while providingan arm portion 104 that may be easily handled by the operator. However,it should be appreciated that the illustration of an arm portion 104having two arm segments 106, 108 is for exemplary purposes, and theclaimed invention should not be so limited. An AACMM 100 may have anynumber of arm segments coupled together by bearing cartridges (and,thus, more or less than six or seven axes of articulated movement ordegrees of freedom).

The probe 118 is detachably mounted to the measurement probe housing102, which is connected to bearing cartridge grouping 112. A handle 126is removable with respect to the measurement probe housing 102 by wayof, for example, a quick-connect interface. As discussed in more detailhereinafter with reference to FIG. 10 et seq., the handle 126 may bereplaced or interchanged with another device such as a laser line probe(“LLP”), which is configured to emit a line of laser light to an objectand to capture or image the laser light on a surface of the object withan imaging device (e.g., a camera) that is part of the LLP, to therebyprovide for non-contact measurement of the dimensions ofthree-dimensional objects. This interchangeable feature and use of anLLP has the advantage in allowing the operator to make both contact andnon-contact measurements with the same AACMM 100. However, it should beunderstood that the LLP may be a standalone device, as described in moredetail hereinafter. That is, the LLP may be fully functional andoperable by itself without any type of connection to the AACMM 100 orsimilar device.

In exemplary embodiments, the probe housing 102 houses a removable probe118, which is a contacting measurement device and may have differenttips 118 that physically contact the object to be measured, including,but not limited to: ball, touch-sensitive, curved and extension typeprobes. In other embodiments, the measurement is performed, for example,by a non-contacting device such as the LLP. In an embodiment, the handle126 is replaced with the LLP using the quick-connect interface. Othertypes of measurement devices may replace the removable handle 126 toprovide additional functionality. Examples of such measurement devicesinclude, but are not limited to, one or more illumination lights, atemperature sensor, a thermal scanner, a bar code scanner, a projector,a paint sprayer, a camera, or the like, for example.

As shown in FIGS. 1A and 1B, the AACMM 100 includes the removable handle126 that provides advantages in allowing accessories or functionality tobe changed without removing the measurement probe housing 102 from thebearing cartridge grouping 112. As discussed in more detail below withrespect to FIG. 2D, the removable handle 126 may also include anelectrical connector that allows electrical power and data to beexchanged with the handle 126 and the corresponding electronics locatedin the probe end 401.

In various embodiments, each grouping of bearing cartridges 110, 112,114 allows the arm portion 104 of the AACMM 100 to move about multipleaxes of rotation. As mentioned, each bearing cartridge grouping 110,112, 114 includes corresponding encoder systems, such as optical angularencoders for example, that are each arranged coaxially with thecorresponding axis of rotation of, e.g., the arm segments 106, 108. Theoptical encoder system detects rotational (swivel) or transverse (hinge)movement of, e.g., each one of the arm segments 106, 108 about thecorresponding axis and transmits a signal to an electronic dataprocessing system within the AACMM 100 as described in more detailhereinafter. Each individual raw encoder count is sent separately to theelectronic data processing system as a signal where it is furtherprocessed into measurement data. No position calculator separate fromthe AACMM 100 itself (e.g., a serial box) is required, as disclosed incommonly assigned U.S. Pat. No. 5,402,582 (“the '582 patent”).

The base 116 may include an attachment device or mounting device 120.The mounting device 120 allows the AACMM 100 to be removably mounted toa desired location, such as an inspection table, a machining center, awall or the floor, for example. In one embodiment, the base 116 includesa handle portion 122 that provides a convenient location for theoperator to hold the base 116 as the AACMM 100 is being moved. In oneembodiment, the base 116 further includes a movable cover portion 124that folds down to reveal a user interface, such as a display screen.

In accordance with an embodiment, the base 116 of the portable AACMM 100contains or houses an electronic circuit having an electronic dataprocessing system that includes two primary components: a baseprocessing system that processes the data from the various encodersystems within the AACMM 100 as well as data representing other armparameters to support three-dimensional (“3D”) positional calculations;and a user interface processing system that includes an on-boardoperating system, a touch screen display, and resident applicationsoftware that allows for relatively complete metrology functions to beimplemented within the AACMM 100 without the need for connection to anexternal computer.

The electronic data processing system in the base 116 may communicatewith the encoder systems, sensors, and other peripheral hardware locatedaway from the base 116 (e.g., a laser line probe that can be mounted inplace of the removable handle 126 on the AACMM 100). The electronicsthat support these peripheral hardware devices or features may belocated in each of the bearing cartridge groupings 110, 112, 114 locatedwithin the portable AACMM 100.

FIG. 2 is a block diagram of electronics utilized in an AACMM 100 inaccordance with an embodiment. The embodiment shown in FIG. 2A includesan electronic data processing system 210 including a base processorboard 204 for implementing the base processing system, a user interfaceboard 202, a base power board 206 for providing power, a Bluetoothmodule 232, and a base tilt board 208. The user interface board 202includes a computer processor for executing application software toperform user interface, display, and other functions described herein.

As shown in FIG. 2A and FIG. 2B, the electronic data processing system210 is in communication with the aforementioned plurality of encodersystems via one or more arm buses 218. In the embodiment depicted inFIG. 2B and FIG. 2C, each encoder system generates encoder data andincludes: an encoder arm bus interface 214, an encoder digital signalprocessor (“DSP”) 216, an encoder read head interface 234, and atemperature sensor 212. Other devices, such as strain sensors, may beattached to the arm bus 218.

Also shown in FIG. 2D are probe end electronics 230 that are incommunication with the arm bus 218. The probe end electronics 230include a probe end DSP 228, a temperature sensor 212, a handle/deviceinterface bus 240 that connects with the handle 126 or the laser lineprobe (“LLP”) 242 via the quick-connect interface in an embodiment, anda probe interface 226. The quick-connect interface allows access by thehandle 126 to the data bus, control lines, and power bus used by the LLP242 and other accessories. In an embodiment, the probe end electronics230 are located in the measurement probe housing 102 on the AACMM 100.In an embodiment, the handle 126 may be removed from the quick-connectinterface and measurement may be performed by the LLP 242 communicatingwith the probe end electronics 230 of the AACMM 100 via the interfacebus 240. In an embodiment, the electronic data processing system 210 islocated in the base 116 of the AACMM 100, the probe end electronics 230are located in the measurement probe housing 102 of the AACMM 100, andthe encoder systems are located in the bearing cartridge groupings 110,112, 114. The probe interface 226 may connect with the probe end DSP 228by any suitable communications protocol, includingcommercially-available products from Maxim Integrated Products, Inc.that embody the 1-Wire® communications protocol 236.

FIG. 3 is a block diagram describing detailed features of the electronicdata processing system 210 of the AACMM 100 in accordance with anembodiment. In an embodiment, the electronic data processing system 210is located in the base 116 of the AACMM 100 and includes the baseprocessor board 204, the user interface board 202, a base power board206, a Bluetooth module 232, and a base tilt module 208.

In an embodiment shown in FIG. 3A, the base processor board 204 includesthe various functional blocks illustrated therein. For example, a baseprocessor function 302 is utilized to support the collection ofmeasurement data from the AACMM 100 and receives raw arm data (e.g.,encoder system data) via the arm bus 218 and a bus control modulefunction 308. The memory function 304 stores programs and static armconfiguration data. The base processor board 204 also includes anexternal hardware option port function 310 for communicating with anyexternal hardware devices or accessories such as the LLP 242. A realtime clock (“RTC”) and log 306, a battery pack interface (“IF”) 316, anda diagnostic port 318 are also included in the functionality in anembodiment of the base processor board 204 depicted in FIG. 3A.

The base processor board 204 also manages all the wired and wirelessdata communication with external (host computer) and internal (displayprocessor 202) devices. The base processor board 204 has the capabilityof communicating with an Ethernet network via an Ethernet function 320(e.g., using a clock synchronization standard such as Institute ofElectrical and Electronics Engineers (“IEEE”) 1588), with a wirelesslocal area network (“WLAN”) via a LAN function 322, and with Bluetoothmodule 232 via a parallel to serial communications (“PSC”) function 314.The base processor board 204 also includes a connection to a universalserial bus (“USB”) device 312.

The base processor board 204 transmits and collects raw measurement data(e.g., encoder system counts, temperature readings) for processing intomeasurement data without the need for any preprocessing, such asdisclosed in the serial box of the aforementioned '582 patent. The baseprocessor 204 sends the processed data to the display processor 328 onthe user interface board 202 via an RS485 interface (“IF”) 326. In anembodiment, the base processor 204 also sends the raw measurement datato an external computer.

Turning now to the user interface board 202 in FIG. 3B, the angle andpositional data received by the base processor is utilized byapplications executing on the display processor 328 to provide anautonomous metrology system within the AACMM 100. Applications may beexecuted on the display processor 328 to support functions such as, butnot limited to: measurement of features, guidance and training graphics,remote diagnostics, temperature corrections, control of variousoperational features, connection to various networks, and display ofmeasured objects. Along with the display processor 328 and a liquidcrystal display (“LCD”) 338 (e.g., a touch screen LCD) user interface,the user interface board 202 includes several interface optionsincluding a secure digital (“SD”) card interface 330, a memory 332, aUSB Host interface 334, a diagnostic port 336, a camera port 340, anaudio/video interface 342, a dial-up/cell modem 344 and a globalpositioning system (“GPS”) port 346.

The electronic data processing system 210 shown in FIG. 3A also includesa base power board 206 with an environmental recorder 362 for recordingenvironmental data. The base power board 206 also provides power to theelectronic data processing system 210 using an AC/DC converter 358 and abattery charger control 360. The base power board 206 communicates withthe base processor board 204 using inter-integrated circuit (“I2C”)serial single ended bus 354 as well as via a DMA serial peripheralinterface (“DSPI”) 357. The base power board 206 is connected to a tiltsensor and radio frequency identification (“RFID”) module 208 via aninput/output (“I/O”) expansion function 364 implemented in the basepower board 206.

Though shown as separate components, in other embodiments all or asubset of the components may be physically located in differentlocations and/or functions combined in different manners than that shownin FIG. 3A and FIG. 3B. For example, in one embodiment, the baseprocessor board 204 and the user interface board 202 are combined intoone physical board.

Referring now to FIGS. 4-9, an exemplary embodiment of a probe end 401is illustrated having a measurement probe housing 102 with aquick-connect mechanical and electrical interface that allows removableand interchangeable device 400 to couple with AACMM 100. In theexemplary embodiment, the device 400 includes an enclosure 402 thatincludes a handle portion 404 that is sized and shaped to be held in anoperator's hand, such as in a pistol grip for example. The enclosure 402is a thin wall structure having a cavity 406 (FIG. 9). The cavity 406 issized and configured to receive a controller 408. The controller 408 maybe a digital circuit, having a microprocessor for example, or an analogcircuit. In one embodiment, the controller 408 is in asynchronousbidirectional communication with the electronic data processing system210 (FIGS. 2 and 3). The communication connection between the controller408 and the electronic data processing system 210 may be wired (e.g. viacontroller 420) or may be a direct or indirect wireless connection (e.g.Bluetooth or IEEE 802.11) or a combination of wired and wirelessconnections. In the exemplary embodiment, the enclosure 402 is formed intwo halves 410, 412, such as from an injection molded plastic materialfor example. The halves 410, 412 may be secured together by fasteners,such as screws 414 for example. In other embodiments, the enclosurehalves 410, 412 may be secured together by adhesives or ultrasonicwelding for example.

The handle portion 404 also includes buttons or actuators 416, 418 thatmay be manually activated by the operator. The actuators 416, 418 arecoupled to the controller 408 that transmits a signal to a controller420 within the probe housing 102. In the exemplary embodiments, theactuators 416, 418 perform the functions of actuators 422, 424 locatedon the probe housing 102 opposite the device 400. It should beappreciated that the device 400 may have additional switches, buttons orother actuators that may also be used to control the device 400, theAACMM 100 or vice versa. Also, the device 400 may include indicators,such as LEDs, sound generators, meters, displays or gauges for example.In one embodiment, the device 400 may include a digital voice recorderthat allows for synchronization of verbal comments with a measuredpoint. In yet another embodiment, the device 400 includes a microphonethat allows the operator to transmit voice activated commands to theelectronic data processing system 210.

In one embodiment, the handle portion 404 may be configured to be usedwith either operator hand or for a particular hand (e.g. left handed orright handed). The handle portion 404 may also be configured tofacilitate operators with disabilities (e.g. operators with missingfinders or operators with prosthetic arms). Further, the handle portion404 may be removed and the probe housing 102 used by itself whenclearance space is limited. As discussed above, the probe end 401 mayalso comprise the shaft of the seventh axis of AACMM 100. In thisembodiment the device 400 may be arranged to rotate about the AACMMseventh axis.

The probe end 401 includes a mechanical and electrical interface 426having a first connector 429 (FIG. 8) on the device 400 that cooperateswith a second connector 428 on the probe housing 102. The connectors428, 429 may include electrical and mechanical features that allow forcoupling of the device 400 to the probe housing 102. In one embodiment,the interface 426 includes a first surface 430 having a mechanicalcoupler 432 and an electrical connector 434 thereon. The enclosure 402also includes a second surface 436 positioned adjacent to and offsetfrom the first surface 430. In the exemplary embodiment, the secondsurface 436 is a planar surface offset a distance of approximately 0.5inches from the first surface 430. This offset provides a clearance forthe operator's fingers when tightening or loosening a fastener such ascollar 438. The interface 426 provides for a relatively quick and secureelectronic connection between the device 400 and the probe housing 102without the need to align connector pins, and without the need forseparate cables or connectors.

The electrical connector 434 extends from the first surface 430 andincludes one or more connector pins 440 that are electrically coupled inasynchronous bidirectional communication with the electronic dataprocessing system 210 (FIGS. 2 and 3), such as via one or more arm buses218 for example. The bidirectional communication connection may be wired(e.g. via arm bus 218), wireless (e.g. Bluetooth or IEEE 802.11), or acombination of wired and wireless connections. In one embodiment, theelectrical connector 434 is electrically coupled to the controller 420.The controller 420 may be in asynchronous bidirectional communicationwith the electronic data processing system 210 such as via one or morearm buses 218 for example. The electrical connector 434 is positioned toprovide a relatively quick and secure electronic connection withelectrical connector 442 on probe housing 102. The electrical connectors434, 442 connect with each other when the device 400 is attached to theprobe housing 102. The electrical connectors 434, 442 may each comprisea metal encased connector housing that provides shielding fromelectromagnetic interference as well as protecting the connector pinsand assisting with pin alignment during the process of attaching thedevice 400 to the probe housing 102.

The mechanical coupler 432 provides relatively rigid mechanical couplingbetween the device 400 and the probe housing 102 to support relativelyprecise applications in which the location of the device 400 on the endof the arm portion 104 of the AACMM 100 preferably does not shift ormove. Any such movement may typically cause an undesirable degradationin the accuracy of the measurement result. These desired results areachieved using various structural features of the mechanical attachmentconfiguration portion of the quick connect mechanical and electronicinterface of an embodiment of the present invention.

In one embodiment, the mechanical coupler 432 includes a firstprojection 444 positioned on one end 448 (the leading edge or “front” ofthe device 400). The first projection 444 may include a keyed, notchedor ramped interface that forms a lip 446 that extends from the firstprojection 444. The lip 446 is sized to be received in a slot 450defined by a projection 452 extending from the probe housing 102 (FIG.8). It should be appreciated that the first projection 444 and the slot450 along with the collar 438 form a coupler arrangement such that whenthe lip 446 is positioned within the slot 450, the slot 450 may be usedto restrict both the longitudinal and lateral movement of the device 400when attached to the probe housing 102. As will be discussed in moredetail below, the rotation of the collar 438 may be used to secure thelip 446 within the slot 450.

Opposite the first projection 444, the mechanical coupler 432 mayinclude a second projection 454. The second projection 454 may have akeyed, notched-lip or ramped interface surface 456 (FIG. 5). The secondprojection 454 is positioned to engage a fastener associated with theprobe housing 102, such as collar 438 for example. As will be discussedin more detail below, the mechanical coupler 432 includes a raisedsurface projecting from surface 430 that is adjacent to or disposedabout the electrical connector 434 which provides a pivot point for theinterface 426 (FIGS. 7 and 8). This serves as the third of three pointsof mechanical contact between the device 400 and the probe housing 102when the device 400 is attached thereto.

The probe housing 102 includes a collar 438 arranged co-axially on oneend. The collar 438 includes a threaded portion that is movable betweena first position (FIG. 5) and a second position (FIG. 7). By rotatingthe collar 438, the collar 438 may be used to secure or remove thedevice 400 without the need for external tools. Rotation of the collar438 moves the collar 438 along a relatively coarse, square-threadedcylinder 474. The use of such relatively large size, square-thread andcontoured surfaces allows for significant clamping force with minimalrotational torque. The coarse pitch of the threads of the cylinder 474further allows the collar 438 to be tightened or loosened with minimalrotation.

To couple the device 400 to the probe housing 102, the lip 446 isinserted into the slot 450 and the device is pivoted to rotate thesecond projection 454 toward surface 458 as indicated by arrow 464 (FIG.5). The collar 438 is rotated causing the collar 438 to move ortranslate in the direction indicated by arrow 462 into engagement withsurface 456. The movement of the collar 438 against the angled surface456 drives the mechanical coupler 432 against the raised surface 460.This assists in overcoming potential issues with distortion of theinterface or foreign objects on the surface of the interface that couldinterfere with the rigid seating of the device 400 to the probe housing102. The application of force by the collar 438 on the second projection454 causes the mechanical coupler 432 to move forward pressing the lip446 into a seat on the probe housing 102. As the collar 438 continues tobe tightened, the second projection 454 is pressed upward toward theprobe housing 102 applying pressure on a pivot point. This provides asee-saw type arrangement, applying pressure to the second projection454, the lip 446 and the center pivot point to reduce or eliminateshifting or rocking of the device 400. The pivot point presses directlyagainst the bottom on the probe housing 102 while the lip 446 is appliesa downward force on the end of probe housing 102. FIG. 5 includes arrows462, 464 to show the direction of movement of the device 400 and thecollar 438. FIG. 7 includes arrows 466, 468, 470 to show the directionof applied pressure within the interface 426 when the collar 438 istightened. It should be appreciated that the offset distance of thesurface 436 of device 400 provides a gap 472 between the collar 438 andthe surface 436 (FIG. 6). The gap 472 allows the operator to obtain afirmer grip on the collar 438 while reducing the risk of pinchingfingers as the collar 438 is rotated. In one embodiment, the probehousing 102 is of sufficient stiffness to reduce or prevent thedistortion when the collar 438 is tightened.

Embodiments of the interface 426 allow for the proper alignment of themechanical coupler 432 and electrical connector 434 and also protect theelectronics interface from applied stresses that may otherwise arise dueto the clamping action of the collar 438, the lip 446 and the surface456. This provides advantages in reducing or eliminating stress damageto circuit board 476 mounted electrical connectors 434, 442 that mayhave soldered terminals. Also, embodiments provide advantages over knownapproaches in that no tools are required for a user to connect ordisconnect the device 400 from the probe housing 102. This allows theoperator to manually connect and disconnect the device 400 from theprobe housing 102 with relative ease.

Due to the relatively large number of shielded electrical connectionspossible with the interface 426, a relatively large number of functionsmay be shared between the AACMM 100 and the device 400. For example,switches, buttons or other actuators located on the AACMM 100 may beused to control the device 400 or vice versa. Further, commands and datamay be transmitted from electronic data processing system 210 to thedevice 400. In one embodiment, the device 400 is a video camera thattransmits data of a recorded image to be stored in memory on the baseprocessor 204 or displayed on the display 328. In another embodiment thedevice 400 is an image projector that receives data from the electronicdata processing system 210. In addition, temperature sensors located ineither the AACMM 100 or the device 400 may be shared by the other. Itshould be appreciated that embodiments of the present invention provideadvantages in providing a flexible interface that allows a wide varietyof accessory devices 400 to be quickly, easily and reliably coupled tothe AACMM 100. Further, the capability of sharing functions between theAACMM 100 and the device 400 may allow a reduction in size, powerconsumption and complexity of the AACMM 100 by eliminating duplicity.

In one embodiment, the controller 408 may alter the operation orfunctionality of the probe end 401 of the AACMM 100. For example, thecontroller 408 may alter indicator lights on the probe housing 102 toeither emit a different color light, a different intensity of light, orturn on/off at different times when the device 400 is attached versuswhen the probe housing 102 is used by itself. In one embodiment, thedevice 400 includes a range finding sensor (not shown) that measures thedistance to an object. In this embodiment, the controller 408 may changeindicator lights on the probe housing 102 in order to provide anindication to the operator how far away the object is from the probe tip118. In another embodiment, the controller 408 may change the color ofthe indicator lights based on the quality of the image acquired by theLLP 242. This provides advantages in simplifying the requirements ofcontroller 420 and allows for upgraded or increased functionalitythrough the addition of accessory devices.

Referring to FIGS. 10-11, embodiments of the present invention provideadvantages for increasing the dynamic range of a laser line probe(“LLP”) 500, which may be part of a measurement unit such as the AACMM100 or part of a non-measurement unit such as a robot or other devicethat moves in a linear and/or a non-linear manner. In the alternative,the LLP 500 may be a hand-held, standalone device not connected with theAACMM 100 or any other device. The LLP 500 may be the same as orsomewhat similar to the LLP 242 as referenced hereinabove with respectto FIGS. 1A, 1B-9 in particular, or may be some other type of laser linescanner in general.

The LLP 500 provides for non-contact measurements of the regular and/orirregular surface features of an object, typically, if connected withthe AACMM 100, in the same frame of reference as that of the hard probe118 of the AACMM 100, as discussed hereinabove. Further, the calculatedthree-dimensional coordinates of the surface points of the objectprovided by the LLP 500 are based on the known principles oftriangulation, as was explained in more detail hereinabove. The LLP 500may include an enclosure 502 with a handle portion 504. The LLP 500 mayalso include an interface 426 on one end that mechanically andelectrically couples the LLP 500 to the probe housing 102 as describedhereinabove. The interface 426 allows the LLP 500 to be coupled andremoved from the AACMM 100 quickly and easily without requiringadditional tools.

Adjacent the interface 426, the enclosure 502 has a portion 506 thatincludes a projector 508 and a camera 510. In the exemplary embodiment,the projector 508 uses a light source that generates a straight line or“stripe” which is projected onto an object surface. The light source maybe, for example and without limitation, a laser, a superluminescentdiode (“SLD”), an incandescent light, a light emitting diode (“LED”), orsome other similar type of light projecting or emitting device. Theprojected light may be visible or invisible, but visible light may bemore convenient and advantageous to use in some cases. As the LLP 500 ismoved by moving the AACMM 100 or by moving the standalone LLP 500 byhand, the projected line or stripe eventually covers the entire surfacearea or a desired portion of the surface area of the object whosesurface physical characteristics are being measured. This is done inrelatively small, cross-section segments or increments, each incrementbeing represented by the projected line or stripe at one location on thesurface of the object.

The camera 510 typically includes a lens or lens system and a solidstate, digital imaging sensor. The lens or lens system is typically usedto filter out ambient light. The digital imaging sensor is typically aphotosensitive array that may be a charge-coupled device (“CCD”)two-dimensional (“2D”) area sensor or a complementarymetal-oxide-semiconductor (“CMOS”) 2D area sensor, for example, or itmay be some other type of light capture device. Each imaging sensor maycomprise a 2D array (i.e., rows, columns) having a plurality of lightsensing elements. Each light sensing element typically contains orcomprises at least one photodetector (e.g., photodiode) that convertsthe captured or sensed light energy (i.e., photons) into an amount ofelectric charge which is stored within the corresponding well withineach light sensing element, where the charge in each well may be addedor integrated and read out as a voltage value. The voltage values aretypically converted into digital values for manipulation by a computeror processor by an analog-to-digital converter (“ADC”). Each digitalvalue represents an amount of brightness at a particular physicallocation on the surface of the object as imaged by the sensor from thelight reflected off of the object surface and captured by the digitalimaging sensor at a particular location within the photosensitive array.Typically for a CMOS imaging sensor chip, the ADC is contained withinthe sensor chip, while for a CCD imaging sensor chip, the ADC is usuallyincluded outside the sensor chip on a circuit board.

Use of these types of digital imaging sensors most often leads torelatively low overall dynamic range in the LLP 500. As statedhereinabove, simply put, the dynamic range of the digital imaging deviceis the range bounded on one end by the amount of relatively brightobject surface portions that the imaging device is capable of accuratelycapturing and bounded on the other end by the amount of relatively darkobject surface portions that the imaging device is capable of accuratelycapturing. Stated another way, the dynamic range of the imaging deviceis the ratio of the largest non-saturating input signal to the smallestdetectable input signal (i.e., such detectable signal beingdistinguishable from an amount of noise typically residing at the lowinput signal levels).

Defined as such, relatively low dynamic range is usually caused by thefact that the digital output of the digital imaging sensor from the ADCis often only characterized by eight binary bits, which results in therelatively small value of 256 different levels of brightness informationbeing able to be provided by the digital imaging sensor. Thus, a typicalreal world object scanned by the LLP 500 most often results in theresulting scanned image being relatively too bright in some areas and/orrelatively too dark in other areas. In other words, the LLP 500 does arelatively poor job of accurately imaging the real world object becausethe digital imaging sensor does not contain enough resolution (i.e.,enough binary output bits) to accurately image or represent both therelatively light and dark areas of the object. Embodiments of thepresent invention described and illustrated herein provide forimprovements or increases in the dynamic range of the LLP 500.

In an exemplary embodiment, the projector 508 and camera 510 areoriented to enable reflected light from an object to be imaged by thephotosensitive array. In one embodiment, the LLP 500 is offset from theprobe tip 118 to enable the LLP 500 to be operated without interferencefrom the probe tip 118. In other words, the LLP 500 may be operated withthe probe tip 118 in place. Further, it should be appreciated that theLLP 500 is substantially fixed relative to the probe tip 118 so thatforces on the handle portion 504 do not influence the alignment of theLLP 500 relative to the probe tip 118. In one embodiment, the LLP 500may have an additional actuator (not shown) that allows the operator toswitch between acquiring data from the LLP 500 and from the probe tip118.

The projector 508 and camera 510 are electrically coupled to acontroller 512 disposed within the enclosure 502. The controller 512 mayinclude one or more microprocessors, digital signal processors, memory,and other types of signal processing and/or conditioning circuits and/orstorage circuits. Due to the relatively large data volume typicallygenerated by the LLP 500 when line scanning an object, the controller512 may be arranged within the handle portion 504. The controller 512may be electrically coupled to the arm buses 218 via electricalconnector 434. The LLP 500 may further include actuators 514, 516 whichmay be manually activated by the operator to initiate operation and datacapture by the LLP 500.

If the LLP 500 is connected with a device such as the AACMM 100 asdescribed hereinbefore, then some or all of the relatively large amountof signal processing required by the LLP 500 may be carried out by theelectronic data processing system 210 within the AACMM 100. The signalprocessing required typically involves processing the raw point clouddata of the object captured by the digital imaging sensor of the camera510 to determine the resulting image of the object through use of, e.g.,triangulation techniques. In this case, some of the data processing mayalso be carried out by the controller 512 within the handle 504 of theLLP 500. In the alternative, if the LLP 500 is a standalone device, thenall of the required signal processing may be carried out by thecontroller 512 and/or by additional signal processing components locatedwithin the handle 504 of the LLP 500.

The laser line probe (“LLP”) in accordance with the aforementionedembodiments of FIGS. 10-11 may be utilized in embodiments of the presentinvention involving LLPs in particular (and line scanners in general)having increased high dynamic range (“HDR”) compared to existing LLPs.Similar to the LLP 500 of FIGS. 10-11, the LLP 500 in accordance withthese increased HDR embodiments of the present invention may include aprojector 508 and a camera 510 and may be connected with an AACMM 100 orsimilar device. In the alternative, the LLP 500 may be a standalone,hand-held type of device.

An issue for all LLPs 500 is obtaining proper exposure control withineach image frame (i.e., each imaged stripe) on relatively high contrastobjects (i.e., an object containing both light and dark areas).Similarly, this issue also occurs with the imaging of a scene havingboth light and dark areas and/or objects within the scene. This is so asto create a relatively accurate image of the object or the scene. Inother words, to obtain relatively accurate 3D coordinates with the LLP,it is desirable to accurately image both the light and dark areas of theobject, along with the mid-range contrast areas of the object inbetween, on the photosensitive array of the camera 510.

Typically, in cameras 510, it is difficult to simultaneously obtain goodimages of dark, mid-range, and light contrast areas of the object orenvironment. This is due primarily to the limited dynamic range of theimaging device (e.g., a camera 510 such as a CMOS or CCD device having a2D photosensitive array of light sensing elements—a.k.a., a digitalimaging sensor). For example, a CMOS photosensitive array may be usedhaving 2048×1024 light sensing elements and operating at 340 frames(“stripes”) per second. The CMOS array generates, for each light sensingelement of the array, a digital value that is approximately proportionalto the illumination level striking each light sensing element. Most LLPs500 commercially available today are configured to do a relatively goodjob in capturing the mid-range contrast areas of an object, but do arelatively poor job in capturing the relatively light and/or dark areasof an object (for “high contrast” objects that have such areas). Thatis, these LLPs have relatively limited or poor overall dynamic range.

Certain embodiments of the present invention include a system orapparatus for, and a method of, creating a relatively high dynamic rangeimage from multiple different colored exposures of an object that arecombined into a single image of the object in each image frame. Otherdifferent embodiments disclosed herein retain the object of improving orincreasing the dynamic range of the LLP 500.

Referring to FIG. 12, in embodiments of the present invention, the LLP500 includes a single color camera 510 that, as mentioned hereinabove,typically comprises a digital imaging sensor which includes a lens orlens system (not shown) and a two-dimensional photosensitive array 1200(i.e., a square-shaped array 1200 comprising a number of light sensorsarranged in rows and columns). The array 1200 comprises a plurality oflight sensing elements such as photodetectors (e.g., photodiodes). MostLLPs 500 commercially available today contain a photosensitive arrayresponsive to the overall amount of light received at all wavelengths.Such an array has differing sensitivity to different wavelengths oflight, but the response of the camera is based on the integrated effectof all the wavelengths of light. Because such an array does not provideany information about the colors of the incident light, it is referredto as a monochrome array. A photosensitive array that provides separatesignals for different colors of light is referred to as a color array,RGB (red, blue, green) array, or RGB image sensor. Thus, one feature ofembodiments of the present invention involves the use of a color array510.

FIG. 12 shows the light sensing elements grouped into a plurality ofsquares 1204 within the array 1200, each square comprising four lightsensing elements. This is done for illustrative purposes to point outthe fact that most modern single-chip, solid-state digital imagingsensors include a color filter array (“CFA”) formed integral therewithfor arranging a mosaic of color filters within the array 1200 ofphotodetectors.

A common type of CFA utilized is a well-known Bayer filter having onered filter, two green filters, and one blue filters. The two greenfiltered light sensors 1208 are diametrically opposed from one another,while the blue sensor 1212 and the red sensor 1216 occupy the other twodiametrically opposed corners of the square. This square layout of theBayer CFA is intended to best take advantage of the human visualsystem's relatively greater ability to discern green detail as opposedto red and blue detail. Each RGB color filter is typically manufacturedas an integral part of each square 1204. Hence for a Bayer filter, asquare 1204 includes four photodetectors, each photodetector covered byone of a red, green, or blue filter. The squares 1204 are repeatedthroughout the array 1200. More information about the Bayer CFA is givenin U.S. Pat. No. 3,971,065 (the “'065 patent”), which is herebyincorporated by reference herein.

In a color image obtained from a color array, each pixel of the imagehas associated with it a color, which may in turn be represented by theamount of red, green, and blue light associated with that color. Thesered, blue, and green colors are obtained from the square 1204, which maytherefore also be referred to as pixel 1204, the pixel 1204 being partof the array 1200.

While embodiments of the present invention have been described herein asusing a Bayer color filter array, digital imaging sensors may be usedhaving types of CFA's other than a Bayer CFA. Also, the CFA may beformed either integral with the photosensitive array of photodetectors1204 or alternatively not integral with the array of photodetectors butrather separated from the array (e.g., a glass mosaic of color filters),with the filters located on top of the photosensitive array 1200.

To minimize unwanted effects of background light, for example, fromoverhead lighting or from sunlight passing through windows, in anembodiment, a filter 1220 having the same color as the projected lightsource 508 may be placed in front of each CFA of the array 1200. Thefilter 1220 may comprise a single filter placed in front of the entirearray 1200 (as shown in FIG. 12). In the alternative, the filter 1220may comprise a plurality of individual filters—each being placed infront of a corresponding pixel 1204 in the array 1200. Thus, inembodiments of the present invention the filter or filters 1220 is/areseparate from the photosensitive array 1200. However, the filter orfilters 1220 may be formed integral within the array 1200, for example,on top of the array 1200 and, thus on top of the CFA.

In an embodiment, a relatively narrow band monochrome blue light source508 (e.g., a laser, an LED, or a superluminescent diode (“SLD”)) isutilized. In other embodiments, a red or green light source is usedinstead. If a blue light source 508 is utilized, then a blue filter 1220is placed in front of each photodetector 1204 in the camera sensor array1200. If a red or a green light source 508 is utilized instead, then acorresponding red or blue filter 1220 is utilized in front of each pixel1204 in the array 1200.

Following the projection of the blue light 1224 toward the surface 1228of an object 1232, the light 1236 reflects back from the object 1232 andstrikes certain pixels 1204 within the array 1200 simultaneously or nearsimultaneously. This generates a response from each of the coloredfilters of the CFA for each frame of the array 1200.

FIG. 15 shows quantum efficiency for R, G, and B filtered areas ofphotodetectors (with filter) in a particular CMOS array. The horizontalaxis of the graph 1500 indicates wavelength in nanometers, with thespectral colors changing from violet, blue, green, yellow, orange, andred as wavelengths move from 400 nm to 700 nm. The vertical axisindicates the quantum efficiency in percent for each of the red, green,and blue regions. Quantum efficiency is the percentage of photonsconverted into electrons for each of the regions. In an idealphotodetector, the quantum efficiency would be 100%. All real detectorshave somewhat lower quantum efficiency. The graph shows that as expectedthe blue filter regions has higher quantum efficiency at the bluewavelengths (near 450 nm) than at the green or red wavelengths.Similarly, green and red filtered regions have greater quantumefficiency at the green and red wavelengths, respectively, than at otherwavelengths. However, the quantum efficiency is greater than zero forevery wavelength in all the filtered regions.

In an embodiment, the light projected from the LLP is blue light havinga wavelength of 450 nm, as indicated by the dashed line 1510. At thiswavelength, the blue filtered region has a quantum efficiency at 1512 ofabout 29%. The green filtered region has a quantum efficiency at 1514 ofabout 8%. The red filtered region has a quantum efficiency at 1516 ofabout 2%.

Consider now the three cases of differing surface reflectance: (1) asurface portion having a high reflectance, (2) a surface portion havinga low reflectance, and (3) a surface portion having an intermediatelevel of reflectance. For the portion of the surface 1228 having a lowreflectance, the amount of light received at the photosensitive array1200 will be relatively weak. In this case, the signal from the bluedetector will be most important since it gives the largest response. Onthe other hand, for the portion of the surface 1228 having a highreflectance, the amount of light received at the photosensitive array1200 will be relatively large, possibly large enough to saturate thephotodetectors of the blue and green filtered regions. In this case, thesignal from the red detector will be most important since it is leastlikely to saturate. For the case in which the surface portion has anintermediate level of reflectance, signals from all three detectors maybe important. To obtain the highest quality measurement, it is desirablethat the ratio of signal to noise from some combination of signals fromthe R, G, and B regions be maximized subject to the constraint that thesignals are taken only from those photodetectors operating within theirlinear regions.

Each photodetector produces an electrical signal in response to theincident light. Within the linear region of a photodetector, the quantumefficiency is a constant. So, for example, a photodetector might have aquantum efficiency of 0.3 (or 30%). This indicates that the probabilityis 0.3 that an incident photon will generate an electron subsequentlyprovided in a signal to image processing electronics. However, asphotons are converted into electrons and an electron well gets full, theprobability of obtaining an electron from an incident photon decreases.In an extreme case, the electron well may overflow. In some types ofarrays, the overflowing electrons may cause blooming by flowing ontoadjacent pixels. In measurements involving an LLP, a certain amount ofnon-linearity can be tolerated. The amount of non-linearity that can beallowed needs to be determined on a case-by-case basis, according to thetechnology and signal processing requirements. However, with this inmind, it can be stated that generally it is desirable to operate each ofthe photodetectors within their linear regions.

An object 1228 may have a variety of different colors over its surface,with each of the different surface colors reflecting different amountsof the projected light 1224. The human eye is not very good atpredicting how much projected light 1224 will be reflected by a surfaceportion having an apparent color. For example, a portion of the surface1228 may appear red to the eye and as expected reflect relatively littleblue light. However, another surface region that appears the same colorto the eye may reflect a relatively larger amount of blue light.

A formula is used to weight the various amounts of light. Weightingfactors w_(R), w_(G) and w_(B) for a CFA having red, green, and bluefilter regions, respectively, satisfy the condition w_(R)+w_(G)+w_(B)=1.Let the corresponding quantum efficiencies be η_(R), η_(G) and η_(B),and the corresponding number of photons entering the array 1200 from thereflected light 1236 be N_(P). If the photodetectors of all the RGBregions are operating in their linear regions and if the CFA is a Bayerfilter, then the effective (weighted) number of electrons N_(E) receivedby a pixel 1204 of the photosensitive array 1200 is

N _(E) =N _(P)(w _(R)η_(R)+2w _(G)η_(G) +w _(B)η_(B)).  (Eq. 1)

The weighting factors are selected to maximize the signal-to-noise ratiowhile avoiding nonlinear effects such as saturation. For cases in whichnonlinearity is a problem, some of the weighting factors may be set tozero. Weighting factors may be a function of the overall amount of lightpassing through the filter 1220 onto the pixels 1204.

An important aspect of the method described herein is that by selectingthe weighting factors appropriately, greater dynamic range than thatordinarily available from the camera system. As explained hereinabove,one cause of limited dynamic range is the limited range of ADCs, whichmay provide only 8 bits (about 48 dB dynamic range) or 10 bits (about 60dB dynamic range). In many cases, the most important factor limiting thedynamic range of a photosensitive array is not the ADC used with thearray but rather the linear range of the photosensitive array itself—inother words the ratio of the largest optical signal that can befaithfully captured to the smallest optical signal that can befaithfully captured. Other factors besides the number of bits of the ADCand the intrinsic linear range of the photodetectors can further degradethe dynamic range of the image obtained from a camera system. When usingthe method described herein, it is usually desirable to increase theoptical power level of the projected light 1224 or, equivalently, toincrease the exposure time for each camera frame. This will result insome of the filter regions being overexposed. For the discussed inreference to FIG. 15, the blue filter region may be overexposed in thiscase. However, the filter regions for green and red have much lowerquantum efficiency and hence are very unlikely to be overexposed.Conversely, by providing a relatively high projected light level orrelatively long exposure, portions of the surface sending relativelysmall amounts of light onto the array 1200 may still be sensitivelydetected with the most sensitive filter region. In the example discussedin reference to FIG. 15, the blue filter region would provide the mostsensitive response. By selecting appropriate weighting factors for theCFA of each pixel 1204, the effective dynamic range may be greatlyincreased beyond that otherwise available. For example, it might bepossible to increase dynamic range to 100 dB or more even using a camerahaving an ADC of only 10 bits (about 60 dB).

Alternative methods for weighting colors for each pixel are describedhereinbelow. However, whatever method is used, the objective is toobtain for each pixel an “effective illumination level” for each pixel.The optical power incident on a pixel for each color is converted by thephotodiode of each color filter region into an electrical signal level.This signal level is converted into a digital level, which is combinedby a processor to obtain an effective illumination level. In anembodiment, Eq. (1) is used to obtain an effective illumination levelfor each pixel. In other embodiments, alternative mathematical methodsare used to obtain an effective illumination level for each pixel. Animportant characteristic of the effective illumination level compared tothe illumination level obtained from a monochrome camera is that in manycases the effective illumination level provides greater dynamic range,thereby enabling more accurate 3D coordinate measurements to be made. Inparticular, it enables materials that are dark, shiny, transparent, orsteeply inclined to be measured while, at the same time, providing theability to measure materials having relatively high reflectance.

Referring to FIG. 13, in certain embodiments of the present invention,each of the blue, red and green image pixel data from the color camera510 is separated from the overall single image for each frame or stripeprovided by the camera 510 and treated as three separate images 1300,1304, 1308 (i.e., red, green and blue images) for each image frame.These three separate images 1300, 1304, 1308 are then processed by ahigh dynamic range algorithm 1312 (an “HDR Processing” function 1312)that is part of embodiments of the present invention. The algorithm maycomprise software executable steps or instructions that are carried outby a processor (e.g., the controller 512 within the LLP 500) thatcomprises the HDR processing function 1312. The processor may comprise,for example, a digital signal processor (“DSP”) or field programmablegate array (“FPGA”). The algorithm 1312, embodiments of which aredescribed in detail hereinafter, combines or “fuses” the three separatecolor images 1300, 1304, 1308 into a single image that is properlyexposed in both the relatively light and dark areas, thereby accuratelyrecreating an image of the object 1232.

Once the single image is generated, well-known triangulation techniquesmay be used to determine the three-dimensional coordinates of each pointwithin the single image, from which the overall image of the object iscreated. In an LLP, the line of light emitted from the projector 508 istypically oriented perpendicular to a plane containing the optical axesof the projector 508 and the camera 510. For a flat surface located aconstant distance from the LLP, the line of light is straight andappears in the same direction in an image of the camera 510. If the flatsurface is kept a constant distance from the LLP but moved farther awayfrom the LLP, the line remains straight but shifts to the side. Bynoting the shape of the line, which is not necessarily straight, the 3Dcoordinates of points on the surface 1228 may be determined. A linebetween perspective centers of the projector 508 and the camera 510 isreferred to as a baseline, and the length of the baseline is thebaseline distance. In general, the calculation used to determine thesecoordinates is based on the baseline distance, the orientations of theprojector 508 and camera 510 relative to the baseline, and on the imageobtained by the photosensitive array of the camera 510. The image of thecamera is converted by electronics into a digital signal, which isevaluated by a processor to determine the 3D coordinates of the surfacepoints. Because methods of triangulation with LLPs are well known in theart, these methods are not discussed further.

In embodiments of the present invention, a projector 508 may producemonochromatic (e.g., blue) light and a color camera 510 may capture theimage of the projected line or stripe of light 1224 after it isreflected off the surface 1228 of the object 1232. An image of theprojected line or stripe pattern is captured by the color camera 510 ina single exposure or frame for each frame or stripe and stored as threevalues per image pixel (i.e., RGB). The three values are the intensitiesfor the red, green and blue color channels captured by the respectivecolor image light sensors 1208, 1212, 1216 in the array 1200. The colorimage is then separated into three separate, new monochrome images 1300,1304, 1308 containing the intensities for each color channel. The resultis a a blue channel image 1308 that is usually overexposed with largeareas of saturation. Also produced are a green channel image 1304 thattends to be correctly exposed and a red channel image 1300 that isunderexposed. The blue channel image 1308 gives a relatively goodexposure on dark object surfaces 1228 and the green channel image 1304gives a relatively good exposure on brighter object surfaces 1228. Theintensities recorded in the red channel image 1300 do not generally givea good exposure on any object surface 1228 because the intensity valuesare relatively low but the high dynamic range images are better when thered channel image 1300 is included.

The three monochrome intensity images 1300, 1304, 1308 from the threecolor channels are then combined or fused together using an algorithm ormethod to produce the single high dynamic range image. There are manyways to carry out this combination or fusion operation using a highdynamic range algorithm or some other method of combination—eithersoftware-based or hardware-based or a combination of both. For example,referring to FIG. 14, an artificial neural network (“ANN”) 1400 may beused to carry out the high dynamic range processing 1312. An ANN 1400works by processing a set of inputs to produce one or more outputs. ANNsare commonly used for classification and pattern matching, but an ANN1400 may be used in embodiments of the present invention for combiningthe three color image intensities 1300, 1304, 1308 into a singlemonochrome intensity image 1404 in the single high dynamic range imageper frame. The inputs to the ANN are the three color channel imageintensities 1300, 1304, 1308 and the output is the single monochromeintensity value 1404. This is processed on a per pixel basis within theimage so that the pixel intensity at location (0,0) in the high dynamicrange image 1404 is calculated from the intensities at location (0,0) inthe individual color channel images 1300, 1304, 1308.

The ANN 1400 typically must be trained before it can be used tocalculate the HDR values in the output image 1404. This is commonlycarried out using training data. In an embodiment, the three monochromeintensity images 1300, 1304, 1308 may be combined using commerciallyavailable HDR software to produce an HDR image 1404 that provides arelatively even exposure on both dark and light surfaces. This outputimage 1404 can then be used to train the ANN 1400 to find a functionthat may process each input set of images 1300, 1304, 1308 to equal thesoftware produced HDR output image 1404. After this training stage iscomplete, the ANN 1400 can then be used with new values for the threemonochrome intensity images 1300, 1304, 1308 and the ANN 1400 willpredict the HDR output image 1404 from the three color channel images1300, 1304, 1308.

In an embodiment of the present invention, the type of ANN 1400 used inthe HDR algorithm may be a multi-layer, perceptron-type ANN. This typeof ANN is typically used for pattern recognition or classification. TheHDR algorithm is essentially a function approximation system that blendsa certain set of inputs to a particular output depending on the datathat the ANN 1400 was trained with. A perceptron ANN takes a set of oneor more inputs and creates a mapping to a set of one or more outputs.Typically, a perceptron ANN contains three or more layers: an inputlayer, one or more hidden layers, and an output layer. However, ANNs canhave just two layers, an input layer and an output layer, but two layerperceptron ANNs are usually unable to solve XOR problems and, as such,are typically only useful in very basic tasks.

In the perceptron ANN each layer usually contains one or more neurons(or nodes) which are connected to all other nodes in the neighboringlayers by a weight value. “Neighboring” typically means that the inputlayer has no direct connection to the output layer, but the hidden layeris connected to both the input and the output layers.

The value at a node is usually calculated as a weighted combination ofthe nodes in the layers previous to the node. This means that the hiddennodes (e.g., H₁, H₂) are calculated using the input layer nodes (e.g.,I₁, I₂, I₃) and weights (e.g., w₁-w₈), while the output layer node value(O₁) is calculated using the hidden node values and weights. This may begiven by the following equations:

H ₁ =I ₁ w ₁ +I ₂ w ₃ +I ₃ w ₅  (Eq. 2)

H ₂ =I ₁ w ₂ +I ₂ w ₄ +I ₃ w ₆  (Eq. 3)

O ₁ =H ₁ w ₇ +H ₂ w ₈  (Eq. 4)

In a multilayer perceptron ANN the node values themselves are not used.Instead, the result of passing the weighted combination through aparticular function is used. The function is non-linear and is designedto model the biological neurons in the brain. The most common functionused is the hyperbolic tangent function (tan h) and this may be used inthe ANN 1400 of the HDR algorithm in embodiments of the presentinvention. This modifies the previous three equations to:

H ₁=ƒ(I ₁ w ₁ +I ₂ w ₃ +I ₃ w ₅)  (Eq. 5)

H ₂=ƒ(I ₁ w ₂ +I ₂ w ₄ +I ₃ w ₆)  (Eq. 6)

O ₁=ƒ(H ₁ w ₇ +H ₂ w ₈)  (Eq. 7)

Where ƒ(x)=tan h(x)

If the output layer nodes pass through the function then the output willbe a binary classifier. However, in an embodiment, the output layer doesnot pass through the function because an output value between 0 and 255possible pixel intensity values is needed, which would not be possibleotherwise.

The weightings on the connections must be calculated before the ANN isof any use. In a perceptron ANN this is typically carried out as atraining or “supervised learning” task, which means that the inputs andoutputs of the ANN 1400 are known and the weights are discovered usingthis knowledge.

The ANN described so far illustrates the approximate configuration ofthe ANN 1400 used in the HDR algorithm. The hidden layer may actuallycontain more nodes than described. For training purposes, there arethree input nodes to the ANN 1400 which may be referred to as R, G andB. These inputs correspond to the three color channel images 1300, 1304,1308 extracted from the single color camera image. Each input node is avalue between 0-255 which is the value range of an eight bit pixel. Theoutput node value is also in the range 0-255 because it is also an eightbit pixel value.

The training of the ANN 1400 may be performed using several sets ofinput images and their corresponding HDR output images created usingcommercial HDR software. This means that for a particular output nodevalue the input node values are known. By applying a technique calledbackpropagation, the weights on the node connections are calculated tominimize the difference between the actual output image and theestimated image created by the ANN 1400. Typically there are two datasets used for training. One dataset is used for calculating theweightings and another set is used to validate the weightings bycalculating the output and comparing the estimate to the actual output.This is done to ensure than the ANN 1400 has not over fit to thetraining data which would mean that it was unusable for any otherdatasets.

In an embodiment of the present invention, the HDR algorithm isimplemented as a parallel algorithm where many image pixels areprocessed at the same time. It is possible to also carry out theprocessing sequentially, but the time required for this will berelatively much higher.

In other embodiments of the present invention, a combination or fusionmethod other than one involving use of an artificial neural network 1400may be used to combine or fuse together the separate images 1300, 1304,1308 into a single composite image 1404. For example, a fusion functionmay keep updating each image pixel of the single composite image if animage pixel is not saturated in its current exposure. A saturationcondition may be defined, for example, as if an image pixel's intensityvalues never exceeded a pre-defined threshold in all phase shiftingimages. As such, the particular image pixel is considered not saturatedin this exposure setting. The term “fusion” in this instance is usedwith regard to how the information obtained from the separate RGB images1300, 1304, 1308 is combined (fused) into a single 3D image coordinate.That is, each of the RGB elements is at nearly the same place on thephotosensitive array 1200. Thus, the three values are fused into asingle 3D value, rather than calculating 3D coordinate values for each.This may be carried out using a weighting algorithm in which those 3Dvalues for which the voltage levels are in the desirable range are givendifferent weightings than the weightings for the 3D values for which thevoltage levels are too high or too low. Another possible fusion methodmay be based on normalization.

In other embodiments of the present invention, instead of using threeseparate images (i.e., red, blue and green) 1300, 1304, 1308, each pixel1204 of the array 1200 may be analyzed (e.g., compared to one another)and the one of the red, green and blue light sensors of the pixel 1204of the photosensitive array 1200 having a certain type of appropriateresponsivity to the projected blue monochrome light may be selected, forexample, to give a well level nearest the full well capacity withoutbeing saturated.

In an alternative embodiment of the present invention, instead of usinga single color camera 510 as part of the LLP 500, the LLP 500 mayincorporate three color cameras 510. A first camera 510 may be utilizedto respond to red light, a second camera 510 may utilized to respond toblue light, and a third camera 510 may be used to respond to greenlight. The desired response from each camera 510 may be achieved byusing an appropriate color filter 1220 located in front of thephotosensitive array 1200 in each camera 510. As in the single cameraembodiments disclosed hereinabove, the response of each of the threecameras 510 is compared to one another to select those levels that areoptimal, or the response values may be fused using methods describedabove. 3D values are obtained from each of the image points, and thesemay be integrated into a single 3D image. Whichever method is used, theresponse curves for R, G, and B should produce attenuations that are inreasonable relative ratios, for example 1:2:4.

For the embodiments having three separate cameras 510 (or two cameras,four cameras, etc.), with each camera 510 having different color filters1220 (i.e., RGB) to respond differently to RGB (or similar wavelengths),a separate triangulation calculation must be carried out for each camera510, and 3D coordinates will be obtained for each image pixel thatcorrespond to each of the cameras 510.

Also, since each of the cameras 510 will have a different field of view,each will cover a slightly different region of the surface 1228 of theobject 1232 being scanned, and the region covered will vary somewhataccording to the distance of the LLP 500 scanner from the object 1232and the angle of the LLP 500 with respect to the object 1232. In thisinstance, one does not necessarily want a one-to-one correspondencebetween light sensors 1204 on the three different photosensitive arrays1200 since these corresponding light sensors 1204 would not necessarilycorrespond to the same region in space.

Instead, consider the embodiment in which, firstly, consider the entireset of image pixels from all three cameras 510 and the correspondingderived 3D coordinates for the three cameras 510. For each of the imagepixels, keep the calculated 3D value if the number of electrons withineach photodetector well is in the desired range—not too few pixels andnot too many. In practice, the number of electrons will be determined bya voltage measured by the ADC in the digital imaging sensor. For thecase of a CMOS sensor array, the ADC will be integrated into the sensoritself. For the case of a CCD array, the ADC will be external componentplaced outside the CCD. In either case, the processor (e.g., thecontroller 512) will know whether each well voltage is within anacceptable range—neither too high (saturated or nearly saturated) nortoo low (in the noisy region).

In an embodiment, the processor 512 may further consider the distancebetween nearest image pixel neighbors in determining whether to discard3D values. For example, if two image pixels are relatively very close toone another in 3D space and one of the image pixels has a very lowvoltage (i.e., in the noisy region), while the other one of the imagepixels has a nearly optimum voltage, it may be that the 3D value for thepixel having the low voltage is discarded. There is also the possibilityof interpolating image pixel values in angle space (or the correspondingtransverse distance space) to obtain a more uniform pattern of 3Dcoordinates. This approach produces relatively clean looking meshedpatterns (“meshed” patterns being a collection of triangles drawnbetween the 3D points).

Instead of using three color cameras 510, three monochrome cameras maybe used instead, in alternative embodiments. Appropriate color filters(i.e., red, green and blue) would be located in front of thephotosensitive array 1200 in each camera—that is, a red filter in frontof a first camera 510, a blue filter in front of a second camera 510,and a green filter in front of a third camera 510. Similar to the colorcamera embodiments described hereinabove, the response of each camera510 may be compared to select the relatively best well levels.Alternatively, the response values from the three cameras 510 may becombined or fused together using the ANN algorithm described hereinaboveor through use of some other method.

In other embodiments of the present invention for increasing the highdynamic range of an LLP 500, the speed of data collection by the LLP 500may be adjusted according to the speed of movement of the LLP 500. Thisembodiment may also be used for other types of line scanners, or evenarea scanners which emit a two-dimensional pattern of light over anarea.

It may be desirable to provide the user of an LLP 500 with a uniform (ornearly uniform) grid or lines of points (in angle or transversecoordinate), each point in the grid or on a line corresponding todifferent distance and 3D coordinate values. If the LLP 500 is movedrelatively slowly by the user (either the LLP 500 being attached to anAACMM 100 or being hand-held), more data is collected than is requiredto obtain such a grid or lines of points. On the other hand, if the LLP500 is moved relatively quickly, less data may be collected than isdesired.

A way to collect a relatively uniform grid or lines of 3D points is toadjust the rate at which data is collected according to the speed of theLLP 500. For the case of an LLP 500 attached to an AACMM 100, the speedof the LLP 500 may be determined based on encoder readings within theAACMM 100, since these are sufficient to determine the six degrees offreedom of the LLP 500 attached to the probe end of the AACMM 100. Thetimes at which data are collected may be determined based on any of thevarious methods—for example, triggering (interrupts) or polling. For thecase in which the LLP 500 is moved relatively too quickly to permit agrid or lines having the desired spacing, a light may be illuminated onthe LLP 500, or another warning indicator given, to indicate to the userthat the LLP 500 should be moved relatively more slowly.

These embodiments of varying the speed at which data is collected fromthe LLP 500 may be independent of the prior embodiments of the presentinvention described hereinabove. In the alternative, the embodiments ofvarying the speed at which data is collected from the LLP 500 may beused with any of the other embodiments described hereinabove forincreasing the HDR of an LLP 500.

Additional embodiments of the present invention involve the use of anintegrated circuit or chip that includes a built-in bilateral filter.Bilateral filtering methods reduce noise in smooth regions whileretaining sharp edges. This type of filtering method is commonly used inpost-processing data, but in this case the capability is included withinthe chip itself.

A second aspect of this chip is that it includes the features of mergingmultiple images into a single high dynamic range image using cameraprocessing. The chip performs the required processing in a few hundredmilliseconds, rather than in a few seconds as in current cameras. Onemethod for improving the dynamic range of laser line scanners or LLPs500 is to change the projected optical power sequentially and thenselect the pixels having the optimum number of electrons in each pixelwell. A method for varying the exposure is also an approach forobtaining increased high dynamic range. The simplest way to varyexposure is to vary the exposure time of the camera. This variation inexposure time may be performed sequentially, as in the embodiment inwhich optical power levels are varied. It may, in some cases, bepossible to perform the HDR calculation in a chip, but in most casesthis will probably not be possible since in the general case eachexposure corresponds to a different position of the LLP 500.

While the invention has been described with reference to exampleembodiments, it will be understood by those skilled in the art thatvarious changes may be made and equivalents may be substituted forelements thereof without departing from the scope of the invention. Inaddition, many modifications may be made to adapt a particular situationor material to the teachings of the invention without departing from theessential scope thereof. Therefore, it is intended that the inventionnot be limited to the particular embodiment disclosed as the best modecontemplated for carrying out this invention, but that the inventionwill include all embodiments falling within the scope of the appendedclaims. Moreover, the use of the terms first, second, etc. do not denoteany order or importance, but rather the terms first, second, etc. areused to distinguish one element from another. Furthermore, the use ofthe terms a, an, etc. do not denote a limitation of quantity, but ratherdenote the presence of at least one of the referenced item.

What is claimed is:
 1. A method for measuring three-dimensional (3D)coordinates of points on a surface of an object, the method comprising:providing a 3D coordinate measurement device, the device including amanually positionable articulated arm portion having opposed first andsecond ends, the second end coupled to a base, the arm portion includinga plurality of connected arm segments, a laser line probe, and anelectrical circuit, each of the arm segments including at least oneposition transducer configured to produce a position signal, the laserline probe coupled to the first end, the laser line probe including aprojector and a camera, the projector separated from the camera by abaseline, the baseline being a line segment, the projector configured toproject a line of light onto the surface, the camera including a lensand photosensitive array, the camera configured to form an image on thephotosensitive array of the line of light projected onto the object, thephotosensitive array having a plurality of pixels, each pixel configuredto provide electrical signal levels for a plurality of colors, thecamera configured to send the electrical signal levels from the pixelsto the electrical circuit, the electrical circuit including a processor;projecting the line of light onto the surface; forming a color image ofthe line of light on the photosensitive array; sending to the electricalcircuit an electrical signal in response to the color image, theelectrical signal containing a signal level for each of the plurality ofcolors for each of the plurality of pixels; determining with theprocessor an effective illumination level for each pixel, the effectiveillumination level for each pixel based at least in part on the signallevel for that pixel for each of the plurality of colors; anddetermining with the processor the 3D coordinates of points on thesurface, the 3D coordinates based at least in part on a length of thebaseline, an orientation of the projector to the baseline, anorientation of the camera to the baseline, the effective illuminationlevel for each pixel, and the position signals.
 2. A laser line probe,comprising; a projector, a camera, and an electrical circuit, theprojector separated from the camera by a baseline, the baseline being aline segment, the projector configured to project a line of light onto asurface, the camera including a lens and photosensitive array, thecamera configured to form an image on the photosensitive array of theline of light projected onto the object, the photosensitive array havinga plurality of pixels, each pixel configured to provide electricalsignal levels for a plurality of colors, the camera configured to sendthe electrical signal levels from the pixels to the electrical circuit,the electrical circuit including a processor, the processor configuredto determine an effective illumination level for each pixel, theeffective illumination level for each pixel based at least in part onthe signal level for that pixel for each of the plurality of colors, anddetermine 3D coordinates of points on the surface, the 3D coordinatesbased at least in part on a length of the baseline, an orientation ofthe projector to the baseline, an orientation of the camera to thebaseline, and the effective illumination level for each pixel.
 3. Thelaser line probe of claim 2, further comprising a handle enclosingelectronic components.
 4. The laser line probe of claim 2, furthercomprising a probe tip.
 5. The laser line probe of claim 2, wherein thephotosensitive array is a color CCD.
 6. The laser line probe of claim 2,further comprising a mechanical coupler configured to attach the laserline probe to a host device.
 7. The laser line probe of claim 6, whereinthe host device is an articulated arm coordinate measurement machine.